Petco often does 1 per gallon cheap way to get tanks. Also feed them garlic and aquarium salt also helps
I always use 1 tablespoon salt per 10 gallon in my water changes. I didn't want to add more then that with my catfish. People on tank talk Facebook page tell me no salt at all for them but I have always put that in with changes and they re fine.. I have also been adding double dose stress coat since this started.
You'll need to figure out what is causing the problems. Fish should never get ich. Environmental stress causes the outbreaks. Something is definitely out of whack with your filtration... Unfortunately adding meds will only make matters worse. Typically ich can be kept under control by raising temps and large waterchanges. No salt or meds needed. I keep a lot of sensitive fish. I don't use salt or meds. In fact, the only time I use meds is when I get wild caught fish in. I quarantine them and use prazipro for internal parasites. Salt and meds will only slow your beneficial bacteria down further, compounding your problems. I feel salt is the most misused item in the hobby. Salt dips work well for removing external parasites. I do not add salt to a display aquarium ever.
Your definitely heading the right direction. Here's the thing with ich...all fish have it. It doesn't manifest itself until the immune system is weakened. A healthy stress free fosh won't show signs of ich. It probably happened when your nitrite spiked, all of your fishes immune systems were compromised and it allowed the ich to take hold. Now that you've got your parameters in check it should clear up.
I've got my fingers crossed! I think a lot had to do with the filter not being big enough. An maybe some over feeding. I cut back on the shrimp for the Oscars. The person I got them from only feed them shrimp an I'm slowly trying to get that down an get them to eat pellets an other stuff. The pet store told me they shouldn't have that much protein. An going from my normal 20 gallon cycle to 60 gallons. I have to get my other have to rig something up so I don't have to climb the ladder so much with 5 gallon buckets. The tank is taller then me. I'm 5 foot nothing an the tank is 5 foot 6 inches tall with the stand. I have to be on my tip toe to feed them. Lol.
Oscars do well with a varied diet. Even occasional fruit! I had one that loved watermelon! He was a pig though, would literally eat anything that hit the water. You can use garden hoses for waterchanges. They sell a sink adapter at most hardware stores, and you can use one to syphon the tank as well. Just run it out a window or to a drain that is lower than your tank.